This inventon relates generally to desoldering apparatus and method and, more particularly, to such apparatus and method employing a fluid pressure differential along a softened solder column.
Individual pin or wire connectors soldered into through holes in circuit substrates or panels frequently must be replaced because of damage or circuit changes. The connectors and through holes are usually located on close center-to-center distances to achieve the required packaging density. Therefore, when selective connector replacement is undertaken, small tools and slow, careful extraction effort are necessary.
In the past, the solder of a selected connector has been usually softened and melted with a fine jet of heated gas such as nitrogen. The gas, being under pressure, also flows over a surrounding area with sufficient heat to soften the solder of neighboring connectors, allowing them to become misaligned. The repeated reheating fosters change in the solder composition through intermetallic growth and raises the temperature of the melting point. Further, if the connector is made of a wettable material, often solder will climb the connector shaft and ultimately interface with the contact surfaces of the connector. To avoid these difficulties, shims, brackets or shields are first installed to support the nearby connectors or to deflect the hot gas. This procedure extends the time necessary to accomplish the connector removal.
Another disadvantage of the usual connector removal processes is that of leaving varying amounts of solder in the through hole. The residue frequently interferes with optical locating procedures that are required when the through hole wall is to be subsequently drilled away and the hole enlarged for a circuit change. Vacuum solder removal tools, exemplified by that in U.S. Pat. No. 3,406,274, and possible reheating are employed to produce the necessary clean holes.